Gas detection based on intra-cavity fiber laser with wavelevnth modulationh and wavelegnth sweep

A low concentration gas detection technique based on intra cavity erbium-doped fiber laser (IEFL) is proposed in this paper combined with wavelength modulation and wavelength sweep. By using wavelength modulation technique (WMT), the second harmonic component of the detected signal is obtained. Combined with wavelength sweep technique (WST), the second harmonic curve of the detected gas absorption lines and FBG array can be detected, with FBG array as wavelength reference. The optimized parameters of the system which maximize the signal-to-noise ratio (SNR) are found. Polynomial fit is adopted to model the nonlinear relationship between the transmission wavelength of the tunable optical filter (TOF) and its driving voltage using the parameters and experimental results of FBG array. Calibration and experimental detection of acetylene concentration are both realized as example. Absorption wavelength detection of acetylene is also realized based on the nonlinear relationship model of the TOF.